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urgent, LPF to suppress the hamonics - RF Cafe Forums
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| nassim1 |
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Post subject: urgent, LPF to suppress the hamonics
Posted: Thu Apr 16, 2009 8:02 am
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Joined: Thu Apr 16, 2009 7:45 am
Posts: 2
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Dear all,
I want to filter the all harmonics above 125MHz using Low pass filter
(BW : 300MHz, specification) but I could not suppress them even I used a good response
LPF . Note that, this harmonics are from mixing an RF signal and an LO signal.
Is an idea about it ??
Thnak you in advance
N
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| nubbage
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Post subject: Re: urgent, LPF to suppress the hamonics
Posted: Mon Apr 27, 2009 7:35 am
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| General |
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Joined: Fri Feb 17, 2006 12:07 pm
Posts: 343
Location: London UK |
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Hi nassim
You will not be able to filter the second harmonic of 125MHz if the -3dB
bandwidth of the LPF is 300MHz.
If your max frequency is 125MHz, then the -3dB cutoff
frequency should be no higher than say 140MHz, in order to ensure that at the second
harmonic (250MHz) the level is well attenuated. There may be other products generated
by the mixer, depending on your system topology. Thus you should ensure that the expected
products in all conditions are above the low frequency -3dB cut-off frequency. What
are all the frequencies present at the mixer ports?
_________________
At bottom, life is all about
Sucking in and blowing out.
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Posted 11/12/2012
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